Polyethylene, polypropylene, and polyolefin polymers have numerous applications in food package, pipes, stretches, bottles and bags. However, the low surface energy and low polarity of polyolefins greatly limit their applications when properties such as printing, painting or adhesion are required.
Conventional methods to improve the adhesion and printability of polyolefins include bulk modification by blending with polar polymers and surface modification by means of physical and chemical treatments. Such treatments include some simple means such as solvent clean-up (or wiping), surface roughening by sand paper, acid treatment and base treatment, to some more sophisticated treatments such as plasma, corona and flame treatments. Some of these treatments lengthen processing time and require a more complicated processing method.
Conventional methods also include adhesive compositions including an organic solvent and a functionalized polyolefin, but a need remains for an adhesive composition with further improved adhesion. Functionalized and non-functionalized styrenic block copolymers have been used in hot melt adhesives and as primers for rubbers. However, they generally do not exhibit sufficient adhesion with polyethylene- or polypropylene-containing polyolefins, when compared to functionalized polyolefins.
A need exists to find simple solutions to improve the adhesion of a polyolefin with itself or with other polar or non-polar substrates. A need further exists to find solutions to provide balanced adhesion, easy processability and flexibility to an article. A need also exists for a primer composition that is easy to process and may be stored or applied to a substrate at room temperature.